Losses

[Sharon]

[SIZE=12pt]Can anyone give me some guidelines/basic assumptions to keep losses straight when dealing with AC and DC machines? Is power to the shaft the same thing as P(out)? Is it true that P(air gap) is equal to P(rotor) only for synchronous machines? When I solve machine problems, I am not confident when handling the losses. Sometimes I figure correctly and sometimes incorrectly. Just want to minimize my chances for error. Thanks in advance.....Sharon[/SIZE]

Also, this forum has been extremely useful to me in my studies this time around. I wish I had known about it back in the Spring. You guys do a phenomenal job!!!!

 

[DK PE]

[SIZE=12pt]Can anyone give me some guidelines/basic assumptions to keep losses straight when dealing with AC and DC machines? Is power to the shaft the same thing as P(out)? Is it true that P(air gap) is equal to P(rotor) only for synchronous machines? When I solve machine problems, I am not confident when handling the losses. Sometimes I figure correctly and sometimes incorrectly. Just want to minimize my chances for error. Thanks in advance.....Sharon[/SIZE]
Also, this forum has been extremely useful to me in my studies this time around. I wish I had known about it back in the Spring. You guys do a phenomenal job!!!!

I would strongly recommend trying to dig up a copy of T. Wildi text Electric Machines, Drives and Power Systems as in my opinion he has some useful diagrams that provide a more practical explanation of where the power is going.

Generally speaking, the mechanical power output of rotor is the electromagnetic power transferred to rotor - electrical losses in rotor. You have to be a bit careful as from an exact point of view, the mechanical power output of the rotor is reduced very slightly by friction and windage losses to get the true output power at the shaft. It is probably safe to say if F&W losses are listed in the problem, use them, otherwise assume negligible.